Secretary of State Hillary Rodham Clinton defends the response to the deadly attack on the Benghazi mission and State Department efforts to increase security during in testimony before the Senate Foreign Relations Committee.

Secretary of State Hillary Rodham Clinton delivered fiery rejoinders Wednesday to Republican critics of the Obama administration's handling of the deadly attack on a U.S. mission in Benghazi, facing off with lawmakers who included potential 2016 presidential rivals.

At times emotional and frequently combative, Clinton rejected GOP suggestions in two congressional hearings that the administration tried to mislead the country about the Sept. 11 attack that killed J. Christopher Stevens, the U.S. ambassador to Libya, and three other Americans.

She insisted the State Department is moving swiftly to strengthen security at diplomatic posts worldwide.

In her last formal testimony before Congress as America's top diplomat, Clinton took responsibility for the department's missteps and failures leading up to the assault. But she also said that requests for more security at the diplomatic mission in Benghazi didn't reach her desk, and reminded lawmakers that they have a responsibility to fund security-related budget requests.

Clinton was at times defiant, complimentary and willing to chastise lawmakers during more than 5 1/2 hours of testimony before two committees.

Her voice cracking at one point, she said the attack and the aftermath were highly personal tragedies for the families of the victims who died - as well as herself.

"I stood next to President Obama as the Marines carried those flag-draped caskets off the plane at Andrews. I put my arms around the mothers and fathers, sisters and brothers, sons and daughters and the wives left alone to raise their children," she told the Senate Foreign Relations Committee at a packed hearing.

She rose to the defense of U.N. Ambassador Susan Rice, who was vilified for widely debunked claims five days after the attack that protests precipitated the raid rather than terrorism. "People were trying in real time to get to the best information," Clinton said.

Sen. Ron Johnson, R-Wis., pressed her on why "we were misled that there were supposedly protests and something sprang out of that, an assault sprang out of that."

"With all due respect, the fact is we had four dead Americans," she said. "Was it because of a protest? Or was it because guys out for a walk one night decided they would go kill some Americans? What difference, at this point, does it make? It is our job to figure out what happened and do everything we can to prevent it from ever happening again, senator."